Impulse timer for x-ray tube systems operable for a preselected number of half-wavesof alternating current cycle



P 1966 L. L. WEISGLASS 3,275,830

IMPULSE TIMER FOR X-RAY TUBE SYSTEMS OPERABLE FOR A PRESELECTED NUMBER OF HALF-WAVES 0F ALTERNATING CURRENT CYCLE Filed Dec. 24, 1963 RELAY n CLOSES ns RELAY 25 1 CONTACTS 20 AND CLOSES TO r26 22 T0 INITIATE X-RAY TUBE ENERGIZED DURING FULL HALF WAVE.

INVENTOR LOU/5 L. WE/SGLASS AT TOR/VE United States Patent 3,275,830 IMPULSE TIMER FOR X-RAY TUBE SYSTEMS OPERABLE FOR A PRESELECTED NUMBER OF HALF-WAVES 0F ALTERNATING CUR- RENT CYCLE Louis L. Weisglass, New York, N.Y., assignor to X-Ray Mfg. Corporation of America, Great Neck, N.Y., a corporation of New York Filed Dec. 24, 1963, Ser. No. 333,110 3 Claims. (Cl. 250-95) The present invention relates to X-ray systems and more particularly to a timer for self-rectified X-ray systems wherein the X-ray tube is energized for a preselected period of time as determined by the alternating current cycle.

Timer systems have long been known to the art wherein an X-ray tube is theoretically energized for a preselected period of time. In such systems, however, the period during which the X-ray tube is energized has been measured in seconds or fractions thereof. Since such timers do not take into account the period required for certain electrical elements, such as relays, switches or the like, to operate and actually cause deenergization of the X-ray tube itself, these timers have been inaccurate especially for very short periods of seconds or fractions thereof. To obviate these difiiculties it is also known in the art to provide a timer arrangement for X-ray systems wherein the X-ray tube is energized for a definite number of cycles of the alternating current source wherein the timing interval for energization of the X-ray tube commences and terminates at the zero points of the sinusoidal voltage cycle. The disadvantage of this latter type system resides in the fact that time is required for the voltage to build up in the system from zero to maximum and during such time deleterious results can occur to various circuit elements since the in-rush current to the primary Winding of the high voltage transformer may be destructively high and considerable arcing and burning away at relay contacts too frequently occurs.

It is accordingly the primary object of the present invent-ion to provide an impulse timer for X-ray systems wherein-the X-ray tube is energized during one or more full half-waves of the alternating current cycle.

Another object of the present invention is the provision of an impulse timer wherein the X-ray circuit is closed at the peak of the alternating current sine wave to thereby keep closure time of the exposure initiating relay constant regardless of length of exposure.

Another object of the present invention is the provision of an impulse timer wherein closure of the X-ray tube energizing circuit occurs at the peak of the alternating current sine wave to minimize relay-contact abuse and assure that the in-rush current of the high voltage transformer primary is at a minimum.

The foregoing objects of the present invention together with other objects which will become obvious to those skilled in the art from the following description are achieved by providing an impulse timer for self-rectified X-ray machines and which timer includes an'energizing circuit having a silicon control rectifier for determining operation of a circuit closing relay. This circuit closing relay is of the shaded coil type having a definite armature inertia and contact spring pressure so that a predetermined time delay exists following energization of its shading coil before complete closing of its contacts occurs. The energizing circuit includes a bank of resistors of progressively increasing ohmic resistance values which govern the charging of a condenser and comprising a constant voltage supply for a time measuring circuit that is operable after a definite number of half-waves of the alternating current cycle, as determined by the selection 3,275,830 Patented Sept. 27, 1966 of the desired resistor of the bank, to energize a circuit opening relay and terminate the timing cycle.

The present invention can be readily understood by reference to the accompanying drawing wherein:

FIGURE 1 is a schematic diagram of the circuitry forming one embodiment which the impulse timer of the present invention may take, and

'FIG. 2 is a graphic illustration of the sinusoidal waveform and showing the points thereon at which the time initiating relay closes its contacts and the exposure terminating relay opens its contacts.

Referring now to the drawing in detail a step-up transformer 5 is shown in FIG. 1 having its primary winding 6 connected to the customary domestic source of supply L1-L2 while its secondary winding 7 producing approximately 250 volts AC. is connected to a full-wave rectifier arrangement made up of four rectifiers 8 which thus delivers at its output terminals 9 and 10 a unidirectional current which in turn charges a condenser 12 to a voltage of approximately 350 volts whereupon such condenser 12 discharges through a resistor 14 to a gas stabilizer tube 13. The energy supplied by condenser 12 under the influence of this gas stabilizer tube 13 thus constitutes a constant voltage supply for a time measuring circuit operable to charge a calibration condenser 15 through a bank of resistors R1 to R8, when the contacts 16 of a timer initiating shaded coil relay 17 are closed.

As seen in FIG. 1, the relay 17 is energized from the supply source L1-L2 upon closure of a switch 18 with half-wave rectified energy by reason of a rectifier 19 included in the energizing circuit for such shaded coil. However, this shaded coil A.C. relay 17 does not close its contacts immediately following energization of its shaded coil winding since the latter, together with its armature inertia and contact spring pressure are so chosen, that regardless of the instant in the sinusoidal wave that the switch 18 is closed to energize the shaded coil of relay 17, it will not operate to close its contacts 16 until the sine wave reaches its peak as shown by the legend in 'FIG. 2. Consequently, by virtue of the X-ray tube itself being self-rectifying it will be energized during the entire reverse shaded half-wave of FIG. 2 following the peak of the forward half-wave when the relay 17 closes its contacts 20 and 22. These latter contacts together with normally closed contacts 23 and 24 of a timing cycle terminating relay 25 complete the power circuit for the X- ray tube energizing transformer (not shown) through conductors 26 and 27. g

The actual time required to charge the calibration condenser 15 is determined by the resistance included in the condenser charging circuit by movement of an adjustable contact 28 into engagement with a preselected one of the progressively increasing ohmic value resistors R1 to R8, and such selection in turn determines the number of halfwaves of the alternating current cycle during which the X-ray tube remains'energized. Resistors 29 and 30 shunted across the DC. supply terminals 9 and '10 constitute a potential divider which regulates the charging voltage on the calibration condenser 15 with the voltage being selectable by movement of an adjustable contact 32 into engagement with various points of the resistor 29 and hence calibrates the discharge of the condenser 15. When this calibration condenser 15 is charged up to approximately volts it will spill over rendering a glow lamp 33, having an inherent definite voltage breakdown characteristic, conductive and discharge through serially connected resistors 34 and 35. The resistor 34 is of such predetermined ohmic value that the discharge time of calibration condenser 15 extends over a minimum period of from 10 to 12 milliseconds, and thus Well beyond the time of one half-wave of the alternating current cycle which lasts 8.3 milliseconds or M2 second, fora purpose hereinafter described.

It will be noted that the winding 36 of low voltage terminating relay 25 is energized through a circuit which extends from a 20 volt tap on transformer primary 6 through contacts 37 of relay 17 when closed, to the wind-. ing 36 and thence to the emitter ofa silicon control rectifier 38 and from the collector thereof back to the end of the primary winding 6. Accordingly, even when con- 'tacts 37 are closed by energization of relay 17 to initiate a preselected timed X-ray exposure by depression of switch 18, terminating relay 25 is'not energized until the silicon control rectifier 38 is made conductive. For the purpose of rendering the latter operative, the gate thereof is connected to a point betweenthe resistors 34 and 35 and a biasing voltage of about 1.5 volts is impressed between i the gate and collector of such rectifier 38 by a resistor 39, with resistor 35 assuring a normally negative biasv on the gate and a condenser 40 shunted across such resistor 39 suppressing spurious line voltage surges.

When exposure initiating switch 18 is depressed. and relay 17 is thus energized and causes, closure of its contacts '16, 20, 22 and 37, the power circuit to the X-ray tube energizing transformer (not shown) will thus be completed, through normally closed contacts 23 and 24 of terminating relay 25 and conductors 26 and:27'as previously herein mentioned, with ,a series connected resistor 42 and condenser 43 suppressing arcing of the relay contacts. Accordingly the X-ray tube .itself will be energized for as many half-waves of the alternating current cycle as occurs during the time that exposure switch 18 remains depressed and until the exposure terminating relay 25 is energized.

During the depression of switch 18 and the ensuing X-ray exposure the calibration condenser 15 is being charged at a voltage as selected by adjusting contact 32 and for a time period determined by the particular resistor Rl'to R8 engaged by the adjustable contact 28. Also.

during the X-ray exposure the previously mentioned biasing voltage of 1.5 volts is applied between the gate with its negative potential and the collector, which thus prevents-the silicon control rectifier 38 from firing to energize realy 25,. However, as soon as the preselected time as selected by adjustable contact 28 to cause charging of calibration condenser 15 through now closed relay contact 16 has expired, such condenser '15 will then be charged to approximately 90 volts and spill over thus rendering glow lamp 33 conductive. This causes condenser 15 .to discharge through resistors 34 and 35 and since the gate of silicon control rectifier 38 is connected thereto the silicon control rectifier 38 breaks down and fires.

The precise instant'of firing of the rectifier 38 depends upon the particular phase of the energizing circuit voltage across the emitter and collector from the 20 volt winding of the transformer primary 6. Should the collector po-- tential be negative at the initial instant of discharging of calibration condenser '15 through glow lamp 33 and re-' sistors, 34 and 35, the negative potential suppliedto the gate of rectifier 38 would not cause firing thereof at that instant. However, since the value of resistor 34 asbefore mentioned is such that the discharge of condenser 15 continues for 10 or 12 miliseconds its negative discharge potential drags out until the next succeeding positive halfwave of the supply voltage across silicon control rectifier 38 and through winding 36 of timer terminating relay. 25,

thus causing the rectifier 38 to fire during such positive half-wave. Break down of silicon control rectifier 38 accordingly continues only for the one half-wave of the alternating current cycle but this is sufiicient time to cause the ensuing energization of winding 36 of low voltage terminating relay 25 with attendant closure of its normally'open contact 44. Closure ,of such contact shorts 23 and 24 not only open to terminate the X-ray exposure at the point on the AC. sine wave as shown in FIG. '2, but remain open so long as the operator continues depression of switch 18 despite termination of the timed X-ray exposure.

Upon release of exposure initiating switch 18 by the operator, relay 17 is of'course deenergized thus opening its then closed contacts 16, 20, 22 and 37 and closing a set of previously opened contacts 45. l Opening of contact 37 thus interrupts the energizing circuittfor the low voltagev winding 36 of exposure terminating relay 25 as well as the contact 16 interrupting the charging circuit for calibration condenser 15.while closure of contact, 45

allows any residual charge on the condenser 15 to'be dissipated through a resistor 46. The reclosing of contacts 23 and 24 upon deenergization of exposure terminating low voltage relay 25 does not again complete the X-ray tube energizing circuit through conductors 26 and 27 at this time because such circuit is then interrupted by the open contacts 20. and 22 of relay 17. 1 g

It should thus, become obvious. to those skilled in the art that a solidstate impulse timer particularly for the timing of self-rectified X-ray tube exposures. has been herein provided wherein the X-ray tube is energized during one or more full'half-waves of the alternating current cycle with the number of such full half-waves determined by the time period during which a calibration condenser is charged to a preselected voltage. Moreover, regardless of the instant that an operator depresses the X-ray exposure initiating switch the energizingrelay does; not actually close the X-ray tube circuit untilthe sinusoidal wave form of the alternating current reaches the peak or crest of a half-wave of one sine to thus commence energization of the X-ray tube at the nextimmedia-tely succeeding. opposite sine half-wave of the alternating current cycle. Also, termination of the X-ray exposure likewise occurs at the peak of the half-wave of the same sine as that during which it was initiated. This accordingly assures energization of the self-rectifying X-ray tube for a preselected definite number. of full half-waves of the alternating current cycle of opposite sine thereby minimize ing relay-contact abuse and assuring that the, in-rush current of the X-ray tube high voltage transformer primary is likewise maintained at'a minimum:

Although one embodiment of the present invention has been hereinishown anddescribed itis to be understood that still further modifications thereof may bemade without departing from the spirit and scope of the appended claimsr I claim:

1. An impulse timer particularly. for the energization of self-rectified X-ray tube systems and operable to. cause 3 comprising:

(a) a circuit for producingia constant unidirectional voltage supply comprising a transformer for charg ing a condenser throughla full-wave'rectifyingarrangement'to a definite direct current potential and including a gas stabilizer tubetoprovide constant voltage and a potential divider to control the supply voltage for a timing circuit;

(b) a time measuring circuit including a calibration condense-r chargeable by said constant unidirectional 'voltage supply circuit, an adjustable resistor ,for selecting the charging-voltage of said'calibration condenser, and .a bank of resistors selectively cons nectable by an operator to said calibration condenser for selecting the total; char-gingper-iod thereof;

(c) means operable to initiate termination of the timing cycle comprising 'a discharge circuit for the .calibra tioncondenser of said time measuring circuitineluding a glow lamp having a definite vo1tagebrea-kdown characteristic and rendered conductive by dis charge ofysaid calibration condenser following lapse of its total charging period and a resistor ofpreselected value to cause the discharge to continue for a period materially in excess of one half-wave of the alternating current cycle, and said discharge circuit being connected to a silicon control rectifier to render the latter conductive by discharge of said calibration condenser during the period said resistor of preselected value receives current;

(d) a relay actuated by rectified current upon closure of its energizing circuit by an operator to cause closure of the X-ray tube energizing circuit only at the peak of a half-wave of the alternating current cycle when said self-rectifying X-ray tube is nonfor operation by said shaded coil relay and including said silicon control rectifier and operable when the latter becomes conductive by discharge of said calibration condenser after the lapse of its preselected 5 charging time to cause deenergization of the X-ray tube following its excitation by a definite preselected number of half-waves of the alternating current cycle.

3. An impulse timer particularly for the energization of self-rectified X-ray tube systems and operable to cause energization of said X-ray tube for a definite preselected number of full half-waves of the alternating current cycle comprising:

conducting and regardless of the instant of energization of said relay, and said relay being also operable to render said constant unidirectional voltage supply elfective to charge the calibration condenser of said timing circuit;

(e) and X-ray exposure terminating means conditioned for operation by said last mentioned operator-controlled means and including said silicon control rectifier and operable when the latter becomes conductive by discharge of said calibration condenser after the lapse of its preselected charging time to cause deenergization of the X-ray tube following its excitation by a definite preselected number of half-waves of the alternating current cycle.

2. An impulse timer particularly for the energization of self-rectified X-ray tube systems and operable to cause energization of said X-ray tube for a definite preselected number of full half waves of the alternating current cycle comprising:

(a) a circuit for producing a constant unidirectional voltage supply comprising a transformer for charg ing a condenser through a full-wave rectifying arrangement to a definite direct current potential and including a gas stabilizer tube to provide constant voltage and a potential divider to control the supply voltage for a timing circuit;

(b) a time measuring circuit including a calibration condenser chargeable by said constant unidirectional voltage supply circuit, an adjustable resistor for selecting the charging voltage of said calibration condenser, and a bank of resistors selectively connectable by an operator to said calibration condenser for selecting the total charging period thereof;

(c) means operable to initiate termination of the timing cycle comprising a discharge circuit for the calibration condenser of said time measuring circuit including a glow lamp having a definite voltage breakdown characteristic and rendered conductive by dis- (a) a circuit for producing a constant unidirectional voltage supply comprising a transformer for charging a condenser through a full-wave rectifying arrangement to a definite direct current potential and including a gas stabilizer tube to provide constant voltage and a potential divider to control the supply voltage for a timing circuit;

(b) a time measuring circuit including a calibration condenser chargeable by said constant unidirectional voltage supply circuit, an adjustable resistor for selecting the charging voltage of said calibration condenser, and a bank of resistors selectively connectable by an operator to said calibration condenser for selecting the total charging period thereof;

(c) means operable to initiate termination of the timing cycle comprising a discharge circuit for the calibration condenser of said time measuring circuit including a glow lamp having a definite voltage breakdown characteristic and rendered conductive by discharge of said calibration condenser following lapse of its total charging period and a resistor of preselected value to cause the discharge to continue for a period materially in excess of one half-wave of the alternating current cycle, and said discharge circuit being connected to a silicon control rectifier to render the latter conductive by discharge of said calibration condenser during the period said resistor of preselected value receives current;

(d) a shaded coil relay having predetermined inertia and spring contact pressure together with a plurality or contacts and energizable only at the peak of a half-wave of the alternating current cycle when said X-ray tube is non-conducting and regardless of the instant of actuation of said relay in response to'initiation by an operator, said relay when energized operating its contacts to cause closure of the X-ray tube energizing circuit at the next full half-wave of the alternating current cycle and also operating additional contacts to render said constant unidirectional voltage supply effective to charge the calibration condenser of said time measuring circuit;

(e) and X-ray exposure terminating means conditioned charge of said calibration condenser following lapse of its total charging period and a resistor of preselected value to cause the discharge to continue for a period materially in excess of one half-wave of the alternating current cycle, and said discharge circuit being connected to a silicon control rectifier to render the latter conductive by discharge of said calibration condenser during the period said resistor of preselected value receives current;

(d) a shaded coil relay having predetermined inertia and spring contact pressure together with a plurality of contacts and energizable only at the peak of a half-wave of the alternating current cycle when said X-ray tube is non-conducting and regardless of the instant of actuation of said relay in response to initiation by an operator, said relay when energized operating its contacts to cause closure of the X-ray tube energizing circuit at the next full half-wave of the alternating current cycle and also operating additional contacts to render said constant unidirectional voltage supply effective to charge the calibration condenser of said time measuring circuit;

(e) and an X-ray exposure terminating relay conditioned for operation by said shaded coil relay contacts and energizable upon said silicon control rectifier becoming conductive by discharge of said calibration condenser after the lapse of its preselected charging time to cause deenergization of the X-ray tube following its excitation by a definite preselected number of half-waves of the alternating current cycle and to interrupt the charging of said calibration condenser by said constant unidirectional voltage supply circuit.

References Cited by the Examiner 

1. AN IMPULSE TIMER PARTICULARLY FOR THE ENERGIZATION OF SELF-RECTIFIED X-RAY TUBE SYSTEMS AND OPERABLE TO CAUSE ENERGIZATION OF SAID X-RAY TUBE FOR A DEFINITE PRESELECTED NUMBER OF FULL HALF-WAVES OF THE ALTERNATING CURRENT CYCLE COMPRISING: (A) A CIRCUIT FOR PRODUCING A CONSTANT UNIDIRECTIONAL VOLTAGE SUPPLY COMPRISING A TRANSFORMER FOR CHARGING A CONDENSER THROUGH A FULL-WAVE RECTIFYING ARRANGEMENT TO A DEFINITE DIRECT CURRENT POTENTIAL AND INCLUDING A GAS STABLIZER TUBE TO PROVIDE CONSTANT VOLTAGE AND A POTENTIAL DIVIDER TO CONTROL THE SUPPLY VOLTAGE FOR TIMING CIRCUIT; (B) A TIME MEASURING CIRCUIT INCLUDING A CALIBRATION CONDENSER CHARGEABLE BY SAID CONSTANT UNIDIRECTIONAL VOLTAGE SUPPLY CIRCUIT, AN ADJUSTABLE RESISTOR FOR SELECTING THE CHARGING VOLTAGE OF SAID CALIBRATION CONDENSER, AND A BANK OF RESISTORS SELECTIVELY CONNECTABLE BY AN OPERATOR TO SAID CALIBRATION CONDENSER FOR SELECTING THE TOTAL CHARGING PERIOD THEREOF; (C) MEANS OPERABLE TO INITIATE TERMINATION OF THE TIMING CYCLE COMPRISING A DISCHARGE CIRCUIT FOR THE CALIBRATION CONDENSER OF SAID TIME MEASURING CIRCUIT INCLUDING A GLOW LAMP HAVING A DEFINITE VOLTAGE BREAKDOWN CHARACTERISTIC AND RENDERED CONDUCTIVE BY DISCHARGE OF SAID CALIBRATION CONDENSER FOLLOWING LAPSE OF ITS TOTAL CHARGING PERIOD AND A RESISTOR OF PRESELECTED VALUE TO CAUSE THE DISCHARGE TO CONTINUE FOR A PERIOD MATERIALLY IN EXCESS OF ONE HALF-WAVE OF THE ALTERNATING CURRENT CYCLE, AND SAID DISCHARGE CIRCUIT BEING CONNECTED TO A SILICON CONTROL RECTIFIER TO RENDER THE LATTER CONDUCTIVE BY DISCHARGE OF SAID CALIBRATION CONDENSER DURING THE PERIOD SAID RESISTOR OF PRESELECTED VALUE RECEIVES CURRENT; 